1. Field of the Invention
The present invention relates to a ferroelectric memory for writing and reading data utilizing the direction of polarization of a ferroelectric.
2. Description of the Related Art
Two types of ferroelectric nonvolatile memory utilizing the reversal of polarization of a ferroelectric having a hysteresis characteristic have been proposed: a one-transistor-one-capacitor (1Tr-1Cap) type wherein one bit is constituted by one switching transistor and one ferroelectric capacitor and a two-transistor-two-capacitor (2Tr-2Cap) type wherein one bit is constituted by two switching transistors and two ferroelectric capacitors.
In the above-mentioned 1Tr-1Cap type or 2Tr-2Cap type ferroelectric memory, a first electrode of each of the ferroelectric capacitors is connected to a bit line through the switching transistor and a second electrode of each of the ferroelectric capacitors is connected to a plate line. The data read and write operations are performed by supplying a first drive signal having a predetermined level to a gate electrode of the switching transistor through a word line and a second drive signal having a predetermined level to the second electrode of the ferroelectric capacitor through the plate line at a predetermined timing.
In the above-described ferroelectric memory, in the data read or the data write operation, the timing of application of a first drive signal for the gate electrode of the switching transistor and the timing of application of a second drive signal for the second electrode of the ferroelectric capacitor are controlled separately.
To achieve an increase in speed, it is necessary to reduce the pulse width. The faster the speed, the more necessary it is to reduce the pulse width.
However, in the above-described ferroelectric memory, since the timings of application are controlled separately, it is difficult to adjust the timings and there is a limitation in the increase of speed.
Also, there is the possibility that the timing of application of the first drive signal for the word line may become earlier or later than a predetermined timing and may therefore become a primary factor of an operational error.